The class of hydroxynitriles is well known. There are numerous processes for their production. The best known process consists of reacting an epoxide with hydrogen cyanide, according to the general equation ##STR2##
The reaction can be carried out with or without a solvent and if needed with a basic catalyst.
In many cases the reaction must, to be sure, because of the low boiling point of the hydrocyanic acid, be carried out in a closed vessel, i.e., under excess pressure.
The hydrogen cyanide is extraordinarily toxic and the operation must be carried out at great expense for the apparatus in order to carry out this reaction in a normal plant.
The carrying out of such reactions in the technology is forbidden in most cases simply because of the extraordinary problems in the transportation of the hydrogen cyanide.
Besides this mode of action assumes that either there exists a hydrocyanic acid plant or a plant which liberates the hydrocyanic acid from its salts.
The last described method which sets free the hydrocyanic acid from its salts can also be undertaken in the plant itself, but here also extensive precautions must be taken.
In several cases specific epoxides can also be reacted with the salts of hydrogen cyanide itself, e.g., with sodium or potassium cyanide, in suitable solvents, yet in these cases water must always be present. An addition of alkali carbonate then sets free a large part of the hydrocyanic acid from the salt.
Such strongly alkaline solutions containing free hydrocyanic acid are quickly colored dark brown to black through polymerizing hydrocyanic acid.
This also cannot be avoided if the aqueous solutions are mixed, e.g. with alcohols.
Hydroxynitriles which are produced in this way are, insofar as they are solid or crystalline, always contaminated with hydrocyanic acid polymers so that the purification of the reaction products creases large trouble.
The method of using the salts of hydrogen cyanide, in contrast to hydrocyanic acid itself, is not generally usable and is forbidden, e.g. in the reaction of .alpha.-epoxides to the corresponding hydroxynitriles.
It has also been proposed already, e.g. to react hydrocyanic acid with acetone to form acetone cyanohydrin, to transport this product to the place of use, to treat it there with alkali and thus to split it again in order to then separate off the hydrocyanic acid by distillation.
All of these procedures always require a great expense.
It has already been proposed by Nazarov, et al (J. Gen. Chem./USSR, 1954, 24, 475 (English Translation), ibid, 1955, 25, 1291) to add hydrocyanic acid with the help of acetone cyanohydrin to an .alpha.,.beta.-unsaturated ketone with the help of acetone cyanohydrin; thereby the procedure was such that the ketone was boiled for several hours with a large excess of cyanohydrin in the presence of an aqueous solution of alkali carbonate in alcohol.
The yields then were only satisfactory if no organic bases were used as catalysts.
The reaction speed can be increased if there is chosen a high excess of acetone cyanohydrin and there is used as catalyst a saturated solution of potassium hydroxide in alcohol. B. E. Betts and W. Davey (J. Chem. Soc. 1958, page 4193) demonstrated this as an example of HCN addition on a chalcone.
In Spanish patent 229,413 (Chem. Abst., Vol, 51, page 9723) there is described the addition of HCN via acetone cyanohydrin on 11-oxoprogesterone.
Acetone cyanohydrin is also an efficient selective cyanidization agent for .alpha.,.beta.-unsaturated carbonyl compounds if the reaction is carried out in the presence of crown ethers and potassium or sodium cyanide in polar or nonpolar solvents (Liotta, et al, Tetrahedron Letters, 1977, page 1117, et seq).
In all the previously described processes, it is a matter of adding hydrocyanic acid to .alpha.,.beta.-unsaturated compounds.
It is the purpose of the present invention to add hydrocyanic acid to an epoxide by a dangerless and environmentally favorable process.